The present invention provides an access-regulating system, apparatus and method for regulating the use of secured equipment. In several cases of particular interest, the secured equipment is a door lock, or the like, and the system is used to regulate access to a secure area, such as a room of a building or a safety deposit box in a bank.
Mechanical locks have been in common use for centuries for limiting access. The misappropriation of a key or of a lock's combination, which allows access by an unauthorized person, has been a problem of long standing with such equipment. Systems that have sought to overcome this problem have failed to provide an adequate solution at an acceptable cost.
As a specific example, hotel owners have long sought a locking system for hotel rooms that would: allow a guest access to a rented room for a limited period; allow a plurality of guests access to a common hotel facility during its hours of operation (e.g., a spa); allow hotel service personnel access to rooms in a controlled and trackable way; and deny room access to a holder of a stolen, copied, or out-of-date key. Ideally, such a system could be installed without requiring extensive re-wiring of the building, and would have no operating costs associated with re-keying locks (e.g., when a guest leaves without turning in his key).
Various electronic security systems are known in which a code stored on a key, card, or other small portable device is recognized by an electronic circuit that controls a door lock. Early systems of this sort used dedicated wiring between a central controller and each lock in order to change the code that a lock would recognize whenever the room was rented out to a new guest. These early systems provided most of the desired features, but at a prohibitive cost (due to the cost of running dedicated signal wiring from a central location to each door lock) and with an intolerable risk of catastrophic failure (i.e., a power failure, or the like, could leave all the doors in the hotel inoperable).
As an improvement on early systems, Downs et al., in U.S. Pat. No. 4,870,400, teach a hotel locking system in which each lock (which may be battery-powered and independent of any dedicated wiring system) recognizes one of several codes sequentially generated by a selected algorithm. A key is generated for a given lock by a master controller that has a record of the previous valid code for that lock (this key may be valid for a limited time if a separate calendar date code is also entered on the key). When the new key is inserted in the lock, electronic circuits in the lock recognize this "next user" code, unlock the door, and reset the lock so that it no longer operates for the "previous user code." If a key is not used (e.g., is issued and then lost before the guest returns to his room), a new key, which is also recognizable by the lock, is issued with a "next-next-user" code. Downs et al. do not provide their lock with a means of writing data on the key and therefore have no way to monitor the use of the key (e.g., by a maid).
Other desired features of a hotel locking system are taught by Genest et al. in U.S. Pat. No. 4,646,080. Genest et al. teach a lock that recognizes a hierarchy of keys, some of which act only to open the lock, and others of which can be used to recode the lock.
Barrett et al., in U.S. Pat. No. 4,988,987, describe a real estate lockbox system that provides each "key" with a fixed code valid for a limited range of calendar dates. As is common in electronic systems, the "key" that Barrett et al. use is a battery powered, computer-controlled device that communicates with the lock circuitry via radio frequency transmission. In Barrett el al's. system both the "key" and the "lock" portions of the system contain computer memory circuits in which data may be written for later retrieval--thus, one can read usage history of a key from the key memory, and usage history of a lock from the lock's memory.
Hyatt and Hall, in U.S. Pat. No. 5,140,317, teach an electronically keyed system that has a microprocessor in both the lock and the key. The key, which carries the power supply to operate the lock, has a code stored in memory. This code is supplied by a master controller and is usable for a single access, whereupon the lock resets to a different code in accordance with an algorithm known to the master controller.
Miron and Neff, in U.S. Pat. No. 5,198,643, teach an electronic locking system that has a lock containing a battery-powered real-time clock and a microprocessor with an access code stored in memory. Their key contains electrically alterable read-only memory (EAROM), but no battery, and provides a means-of carrying an access code from the master controller to a designated lock. Their system uses synchronized real time clocks in each lock and in the master controller. The overall access code in their system is a combination of fixed code elements (e.g., a key access level code or a hotel name code), and re-settable timing data (time of issuance, time of latest authorized access). This system is vulnerable to attack by a thief who obtains a key, reads the data written thereon and generates a new key having the same fixed code elements and appropriate timing data code elements so that the duplicate key coacts with the lock to open a targeted door.
Many modern communication systems rely on pseudo-random, or other, complex sequential codes that change during the course of a message. These coding schemes are designed so that it is very difficult to fathom the code sequence from an intercepted message. In many such systems the sender and receiver of the message have synchronized clocks and both use the same computer algorithm to generate, in a parallel, time-locked fashion, the encoding and decoding keys that are applied to a given message fragment. Coding systems of this sort are well known in the communication art and have been described, inter alia, by W. Wesley Peterson in "Error Correcting Codes" (MIT Press, 1961) and in a chapter entitled "Modulation by Pseudo-Random Sequences" in "Digital Communication with Space Applications" (Solomon W. Golomb, ed., Prentice-Hall, 1964).